Particulate matter, also called particle pollution, consists of microscopic pieces of solids or liquids that are suspended in the air. Sources of this pollution include exhaust gases from automobiles and other internal combustion engine vehicles, road dust from tire and road abrasion, fossil fuel power plants, industrial facilities, construction sites, wood stoves, volcanoes and forest fires.
Inhaling particulate matter can be harmful to health. Larger particles with a diameter of ten microns (PM10), can irritate the eyes, nose, and throat. Smaller particles, with a diameter of 2.5 micrometers or less (PM2.5), are more dangerous because they can penetrate deeper into the lungs and even enter the bloodstream and brain and can thus cause respiratory disease, heart attacks, cancer and premature death.